The present invention resides in the field of mechanical engineering, in particular micromechanics, and can be used with functional elements which are used to convey or influence fluids.
The invention can be used particularly advantageously in medical technology, where it is made to work, in particular in invasive medicine, on body fluids, for example blood. For this purpose, micromechanical functional elements, for example pumps, are known, which have such a small construction that they can be conveyed through a blood vessel. Pumps of this type can be operated within a blood vessel itself or in a ventricle.
In order to enable a particularly efficient and effective operation, it is known to design such functional elements such that they have a compressed state in which they can be moved through a bloodstream and also an expanded or dilated state which they can adopt for example after introduction into a ventricle or another body cavity. In this expanded state, for example a pump can then have a rotor and a housing which apply sufficient pump power by means of their size and nevertheless can be introduced in the compressed state into the body and removed again therefrom.
Various techniques are known for compressing or expanding such pumps. For example, so-called shape memory materials in the form of alloys are used, one of which is known by the trade name Nitinol, the corresponding components generally adopting various geometric shapes as a function of temperature. The type of construction can be designed such that a first dimensional size is adopted in a first state of a Nitinol frame, whilst a second size is achieved in a second state at a different temperature. For example in the case of pumps, both the housings and the rotors can in principle be compressed and expanded in this way.
However pumps without rotors which transport a fluid by expulsion by means of volume changes are also known. Such a pump is known for example from DE 10 2007 012 817 A1. Use of such a toroidal pump is known there for assisting the heart, the pump being inserted in a blood vessel. The housing has a stable external shape but can be folded up. The whole pump is designed as a double chamber hollow body, a balloon which can vary within the housing effecting the volume change of a pump volume and hence suctioning in and expelling fluid. With respect to the type of housing and in addition in what manner this housing is compressible, nothing is stated in the document.
A pump is known from the public inspection document DE 4124299 A1, which has a housing which can be filled with a fluid and consequently stiffened and also a conveying element which can be pumped up therein so that alternately fluid in the housing interior can be suctioned in and expelled.
Similar pumps are known from U.S. Pat. No. 5,820,542 and U.S. Pat. No. 5,827,171.
U.S. Pat. No. 5,928,132 discloses a pump with an expandable housing which can be stiffened by means of fluid-filled cavities.